Amine-functional monoethylenic monomers, acrylic copolymers and aqueous coating compositions containing the same

ABSTRACT

Monoethylenically unsaturated polymerizable monomers carrying a plurality of ketimine-blocked primary amine groups are disclosed. These are preferably provided by reacting an organic diisocyanate with the single secondary amine group of a ketimine-blocked diprimary amine carrying a single secondary amino hydrogen atom and then reacting a monohydric acrylate with the other isocyanate group. These monomers are polymerizable to provide copolymers with other monoethylenically unsaturated monomers, and especially acrylate-functional monomers, in which the amine groups remain blocked. These amine groups become unblocked when the copolymers are dispersed in water to form various types of aqueous coating compositions.

DESCRIPTION

1. Technical Field

This invention relates to latent primary amine-functional monoethylenicmonomers, and especially urethane acrylates, and it includes acryliccopolymers containing these monomers as well as aqueous coatingcompositions containing these copolymers. Amine-functional copolymers inwhich the amine functionality is blocked for release in the presence ofwater have not hitherto been practicably available, and are madeavailable by this invention.

2. Background Art

Monoethylenically unsaturated copolymerizable monomers having primaryamine functionality are rare, especially those with acrylicunsaturation. In part this is because the amino hydrogen groups reactwith acrylic unsaturation in a Michael-type addition reaction whichconsumes the unsaturation. Even though the methacrylic functionalitybetter resists the Michael-type reaction, the usual amino-functionalmethacrylates in commerce are tertiary amines.

In this invention the primary amino hydrogen atoms are blocked forrelease in the presence of water, and thus resist Michael addition priorto polymerization which would prematurely and undesirably eliminate theethylenic unsaturation, especially if the unsaturation is acrylic. Theabsence of water also prevents premature reaction with other resins,such as epoxy resins, in organic solvent medium, and this allows one toplace the polymers of this invention into coating compositions which arecomplete except for the introduction of water or solublizing acid, orboth.

On the other hand, when these polymers with their blocked primary aminegroups are placed in aqueous medium, the primary amine groups becomeunblocked and reactive. However, in the aqueous medium one can protonatethe amine groups with a volatile acid, like acetic acid, and thusmaintain much of the stability which is desired prior to use.

As will be evident, once the aqueous coating compositions are depositedupon a substrate and the water and solvent components evaporate, thevolatile acid also evaporates. In the absence of the stabilizing acid,the primary amine groups are rapidly reactive, and this allows the cureto proceed either at room temperature, or more rapidly at elevatedtemperature.

Copolymerizable monoethlenically unsaturated monomers containing aketimine-blocked primary amine group are known, as described in U.S.Pat. No. 3,497,485 issued Feb. 24, 1970 to W. D. Emmons, and these havebeen copolymerized with other monomers and used in aqueous medium.However, the known systems have not received commercial acceptance forseveral reasons.

First, the prior ketimine-functional monoethylenic monomers were madefrom linear polyethers which are primary amine-terminated at one end andhydroxy-terminated at the other end. These are not very available incommerce, and it is desired to proceed using more readily availablereactants.

Second, the prior ketimine-functional monoethylenic monomers could onlybe made by transesterification, and this is not the easiest reaction, asdescribed in the Emmons patent.

Third, transesterification is not a clean reaction, leaving unreactedester and disturbing the ketimine block. It will be understood,especially when acrylate unsaturation is present, that momentaryunblocking can lead to undesired Michael addition.

Accordingly, another feature of the invention is to avoid the difficulttransesterification reaction needed by Emmons, especially by usingreactions which are much easier to carry out.

Fourth, the ester structure produced by Emmons is well known to behydrolytically unstable, and the ketimine-blocked polymers desiredherein are used in aqueous medium which is either acidic or basic toprovide polymer dispersibility. Thus, the products of this invention arenormally used under conditions provoking hydrolytic instability, whichis exactly where the Emmons esters are inadequate. It is desired hereinto use linkages having greater hydrolytic stability.

Moreover, the Emmons product brings in only one ketimine group for eachethylenically unsaturated group. This is not very economical and itminimizes the cross-link density. The Emmons patent does not hint at howa monoethylenic monomer containing a plurality of ketimine-blockedprimary amine groups might be provided.

DISCLOSURE OF INVENTION

In accordance with this invention, a monoethylenically unsaturatedpolymerizable monomer is provided carrying a plurality ofketimine-blocked primary amine groups. The monoethylenic unsaturation ofsaid monomer is preferably provided by the acrylate or methacrylategroup, and most especially the acrylate group, though other unsaturatedgroups may also be used, such as maleic unsaturation, allylicunsaturation and styryl unsaturation. All the primary amine groups mustbe ketimine-blocked in this invention, as is illustrated by thepreferred reactant, diketimine-blocked diethylene triamine.

Using diethylenetriamine as a prime illustration in this invention, itis blocked by ketimine formation with each of its two primary aminegroups in conventional fashion. This provides a monosecondary aminecontaining two ketimine-blocked primary amine groups. This diketiminewith its single amino hydrogen atom is then reacted to introduce asingle ethylenically unsaturated group. This can be done by reactionwith maleic anydride or methacrylic acid to form a carboxylic acidamide, or it can be done by reaction with an ethylenically unsaturatedepoxide, like allyl glycidyl ether or a monoester of acrylic acid with adiglycidyl ether of a bisphenol, or a monoether of hydroxyethyl acrylatewith a diglycidyl ether of a bisphenol. In this invention it is foundthat preferred products are obtained using isocyanate-functionalcompounds to combine the ketimine-blocked primary amine groups withacrylate or methacrylate unsaturation via the hydrolysis-resistanturethane and urea groups. Both groups form rapidly at moderatetemperatures from reactions producing a very clean and highly usefulmonoethylenic product.

The above reactions are all straightforward and well known.

The urethane-forming reaction is particularly preferred and isillustrated by again using diketimine-blocked diethylene triamine asillustrative. This monosecondary amine is reacted with one molarproportion of an organic diisocyanate which may be either aliphatic oraromatic, but which is preferably of resinous nature because the twoisocyanate groups are at the ends of a polyurethane. The result is thatone of the two isocyanate groups in the selected diisocyanate is reactedwith monosecondary amine containing two ketimine-blocked primary aminegroups, and this leaves the other isocyanate free for reaction with amonohydric acrylate or methacrylate, such as 2-hydroxyethyl acrylate.

As a matter of interest, the above reaction sequence is essential usingacrylate unsaturation, but with other unsaturation, such as styryl orallyl unsaturation, one can react the unsaturated monoisocyanatedirectly with the secondary amine.

The product is a monoacrylate or other mono-unsaturated urethane whichcontains two ketimine-blocked primary amine groups. However, and sincethe primary amine groups are blocked, the acrylate and/or methacrylatefunctionality which may be present is protected from being consumed byMichael-type addition reactions.

The above protection of the reactive ethylenic unsaturation applies notonly to the monomer as it awaits polymerization, but also to themixtures of monomers which one might wish to copolymerize and which willcontain all sorts of ethylenic unsaturation, usually including the verysensitive acrylate unsaturation. This would be true in radiation-curingcompositions where acrylate monomers and oligomers are usually preferredbecause of their high reactivity in such cures, but also to diversepolymerizations, such as solution polymerizations, where thepolymerization is carried out slowly at elevated temperature in thepresence of a free-radical polymerization initiator, such as benzoylperoxide or the like, to provide solvent-soluble copolymers. This latterpolymerization is especially preferred to provide soluble copolymers inwater-miscible volatile organic solvents which facilitate the subsequentdispersion of such copolymers into water with the aid of a volatilesolubilizing acid, illustrated by formic acid, acetic acid, glycolicacid or dimethylol propionic acid.

As a result, the protection of acrylate unsaturation from the aminohydrogen atoms is important regardless of whether the monoethylenicallyunsaturated ketimine-blocked monomer contains acrylate unsaturation ornot.

While one can start with an organic diisocyanate which is then reactedwith either of the two monofunctional reactants (the monosecondary amineor the acrylate- or methacrylate-functional monoalcohol), when acrylategroups are not present, special precautions are needed when acrylatemonomers are used. To illustrate a more complex reaction sequence inthis invention, one can react either reactant with a startingdiisocyanate, and then react with some difunctional material, such as adiol like polypropylene glycol having a molecular weight of 400, andthen react the reaction product with a diisocyanate which is reactedwith the other reactant either before or after its reaction with thediol reaction product. Of course, one should not add the amine reactantwhen the acrylate group is present.

Many process variations will be evident to those in the art, and thepolyurethane monomers with the preferred monosecondary amines are bestdefined by their structural formula which is as follows: ##STR1## inwhich:

R₁ is a divalent organic aliphatic or aromatic molecule connecting thetwo isocyanate groups the residues of which are shown;

R₂ is C₂ -C₄ alkylene, preferably ethylene;

R₃ is a monoethylenically unsaturated carboxylic acid forming an esterwith R₂ ;

R₄ is C₂ -C₄ alkylene, preferably ethylene; and

Z is the residue of an aliphatic ketone forming a ketimine with thenitrogen atom.

The monomers described above can be copolymerized with otherpolymerizable monoethylenically unsaturated monomers in any desiredfashion, albeit conventional solvent solution copolymerization ispreferred. Since the ketimine groups are water-sensitive, the organicsolvents used should be water free to prevent premature unblocking ofthe amine groups. The solvent solution copolymerization is entirelyconventional and will not be discussed herein except to point out thatthe monomers are dissolved in the solvent and the polymer which isformed is preferably also soluble in the solvent and thecopolymerization is carried out in the presence of a free-radicalpolymerization initiator, benzoyl peroxide being typical of theinitiators which release free radicals upon being heated topolymerization temperature.

Turning to the monoethylenically unsaturated monomers which arecopolymerized in organic solvent solution to provide the solublecopolymers which are primarily contemplated herein, these will include"nonreactive" monomers and may also include reactive monomers unless theprimary amine groups employed herein are to be the only ones reliedupon. It is usually preferred to include reactive groups such as hydroxyor carboxy groups. The purpose is to provide a polymer containing groupswhich can be used for cure, either because they are reactive undernormal curing conditions with themselves or other groups in the polymer,or because they are reactive under normal curing conditions withreactive groups supplied by an extraneous curing agent such as anaminoplast, phenoplast or blocked polyisocyanate curing agent, all ofwhich are themselves well known.

The term "nonreactive" as applied to a monomer denotes the absence inthe monomer of functional groups, other than the single polymerizableunsaturated group, which will react under the contemplated conditions ofpolymerization and cure. Normally, this means that the single ethylenicgroup is the only potentially reactive group present. Suitablenonreactive monomers are illustrated by styrene, vinyl toluene, C₁ -C₈alkyl esters of monoethylenically unsaturated acids, like methylmethacrylate, a butyl acrylate or methacrylate, or 2-ethylhexylacrylate, vinyl acetate, acrylonitrile, and the like. In the preferredpractice of this invention, from 3% to 35%, preferably from 5% to 20% ofthe copolymer is constituted by the amine-functional monomers of thisinvention, from 0% to 25% is constituted by an hydroxy-functionalmonomer like 2-hydroxyethyl acrylate, from 0% to 25% is constituted by acarboxy-functional monomer, like acrylic acid or methacrylic acid, andthe balance of the copolymer, usually at least 60% thereof, isconstituted by nonreactiave monomers such as styrene and/or vinyltoluene, alkyl acrylate or methacrylate, such as methyl methacrylate,butyl acrylate or 2-ethylhexyl acrylate.

The preferred curing agents used herein, whether within or without theamine polymer, contain the methylol group (which is carried by nitrogenin the aminoplast resins). These cure by a condensation reaction inwhich alcohol is removed. This reaction is catalyzed by the presence ofacid, and the acrylic acid containing copolymers which may be formedherein likely have this function. The carboxyl group is also reactivewith the methylol group, and this reaction eliminates any excess aciditywhich may be included in the amine polymer.

The curing agents are desirably methylol functional, such as aminoplastresins or phenoplast resins, but blocked polyisocyanates are alsouseful, and all of these are well known for the cure of aqueouscoatings, including electrocoatings.

The aminoplast resins which may be used herein are illustrated byhexamethylol melamine, but partially ethylated or partially butylatedderivatives thereof are also useful. Urea-formaldehyde andbenzoquanamine-formaldehyde resins are also useful in a waterdispersible form, this usually being attainable by forming methoxyethers with the reactive methylol group.

The phenolic resins which may be used as curing agents herein may bewater soluble, but they are more desirably solvent soluble materialswhich disperse in acidic resin aqueous dispersions, such as thosedisclosed in Sekmakas and Plaisance U.S. Pat. No. 4,447,982. Suitableaminoplast resins and bisphenol-formaldehyde resins which may be usedare disclosed in Sekmakas and Shah U.S. Pat. No. 4,265,795 issued May 5,1981. Appropriate bisphenol-formaldehyde resins are further illustratedin Edward J. Murphy U.S. Pat. No. 4,278,579 issued July 14, 1981.Production of the bisphenol-formaldehyde ethers which are preferred isfurther illustrated in U.S. Pat. No. 4,310,653 issued Jan. 12, 1982 toJohn J. Krajewski and Murphy.

When an N-methylol functional monomer, such as acrylamide ormethacrylamide which can be methylolated either before of aftercopolymerization, is included within the amine-functional polymer, it isdesirably used in an amount of from 5% to 40% of the copolymer,preferably from 20% to 35%, and even when it is used, an external curingagent may still be used, albeit in smaller amount than if the N-methylolfunctional monomer were not included within the amine-functionalpolymer.

The blocked polyisocyanate resins are well known for curingamine-functional resins, and are illustrated by 2-ethylhexanol-blockedtoluene diisocyanate or isophorone diisocyanate. These will disperse inthe aqueous medium for codeposit with the amine polymers and unblockwhen the coatings are baked.

As will be appreciated, the aminoplast, phenoplast and blockedpolyisocyanate resins are all stable in the aqueous medium even thoughthe presence of water has served to unblock the primary amine groups inthe polymer. The deposited coatings are then baked to cure the same inconventional fashion, the baking temperature being a function of thecure selected, the catalysts used and the temperature at which thepolyisocyanate unblocks.

However, one can also use a polyepoxide for cure, and now the mixture ofpolyepoxide and unblocked amine polymer in the aqueous medium isunstable. The stability is reasonably good because of the presence ofacid, such as acetic acid, to help disperse the amine polymer becausethe acid functions to protonate the amine groups, thus making them lessreactive in the aqueous medium. However, and when the water, solvent andvolatile acid evaporate, the amine functionality becomes highly reactiveand the cure can take place in a practical period of time at roomtemperature, or it can be speeded with moderate heat.

While ketimine-blocked diethylene triamine has been used and ispreferred because it provides a blocked ketimine which is amonosecondary amine, one can also use ketimine-blocked triethylenetetramine which forms a diketimine containing two secondary aminegroups. This can be reacted with two molar proportions of a diepoxide ora diisocyanate, to provide a diepoxide or diisocyanate-terminatedintermediate. One of these terminal epoxide or isocyanate groups canthen be terminated with acrylate unsaturation as taught herein, and theother one can be left unreacted or blocked with a volatile alcohol orreacted away in any desired fashion.

When the second isocyanate group is reacted with a volatile blockingagent, such as a lower alcohol, like isopropanol, butanol or 2-ethylhexanol, the monomer now contains both blocked primary amine groups andblocked isocyanate groups. When such a monomer is polymerized, itprovides both of these groups in a solvent-soluble copolymer. When thatcopolymer is now dispersed in water as taught herein, it will acquireprimary amine groups, but the isocyanate group remains blocked until thecoating is baked to remove the blocking groups, e.g., the alcohol. Atthat time the cure will be very rapid because primary amine groups andisocyanate groups are highly reactive.

The preferred acids for solubilizing the amine polymers are volatileorganic acids, such as formic acid, acetic acid, glycolic acid, anddimethylol propionic acid. Carbonic acid is also useful. Inorganic acidswhich do not damage the deposited film, like phosphoric acid, may alsobe used. Acids which vaporize or decompose are particularlycontemplated.

The solubilizing acids may be present during polymerization, as taughtin U.S. Pat. No. 4,195,147, or added later.

The partially or fully neutralized amine polymers are dispersed inwater, together with a curing agent if needed, and enough water is usedto provide aqueous dispersions at appropriate solids content forconventional coating applications (spray, direct or reverse rollcoating) or at lower solids for electrocoating (from 3% to 20%, morepreferably from 5% to 15%). The water miscible volatile organic solventused in the polymerization is retained and the presence of the solventhelps to provide the stable dispersions needed for durable aqueouscoatings, especially for electrocoating.

When carboxylic acid is present in the copolymer, then the product isamphoteric and may also be dispersed in water with a volatile base, suchas ammonia or an amine like dimethyl ethanol amine. This providesanionic polymers in the aqueous medium and these can be electrodepositedupon the anode.

In conventional electrocoating practice, grounded conductive objects areimmersed in the electrocoating bath and a unidirectional electricalcurrent is passed through the bath and through the grounded object ascathode or anode to cause the polymers, curing agent and any pigmentdispersed in the bath to be electrodeposited upon the cathode or anode.

The voltages used for electrodeposition, the washing procedures employedto rinse off the bath material which remains on the electrocoated object(which is usually ferrous metal) and the baking conditions generallyapplicable to the various amine polymer systems in use, are all known inthe art and are illustrated in the example of preferred practice herein.

All proportions herein and in the accompanying claims are by weight,unless otherwise specified.

The invention is illustrated in the Examples which follow:

EXAMPLE 1

154.00 grams of polypropylene glycol having a number average molecularweight of 1000, 20.16 grams of diethylene glycol, 40.00 grams ofpolyethylene glycol having a number average molecular weight of 4000 and71.39 grams of methyl ethyl ketone (water-free urethane grade productsis always used in these examples) are mixed in a 1 liter flask equippedwith nitrogen purge, overhead stirrer and reflux condenser including adrying tube. This mixture in the flask is then heated to 75° C.

0.10 grams of dibutyltin dilaurate is then added to the hot mixturefollowed by the dropwise addition over a period of 1 hour of a solutionof 140.37 grams of isophorone diisocyanate and 46.79 grams of methylethyl ketone. The reaction is continued until a final NCO value of 5.76is obtained and the mixture is then cooled to 30° C. to provide anisocyanate-terminated polyurethane.

A solution of 59.32 grams of a methyl ethyl ketone-blocked diethylenetriamine in 19.77 grams of methyl ethyl ketone is then added dropwiseover 15 minutes. The resulting mixture containing the urea formed byreacting the ketone-blocked diethylene triamine with theisocyanate-terminated polyurethane is then heated to 50° C. whereupon28.21 grams of 2-hydroxyethyl acrylate and 9.40 grams of methyl ethylketone are slowly added over a 10 minute period to form a urothane withthe remaining isocyanate functionality. The reaction mixture is held at50° C. until no free isocyanate is detectable by infrared analysis. Thenthe solution is diluted to 60% nonvolatile solids content by theaddition of 147.25 grams of isopropanol.

The methyl ethyl ketone-blocked diethylene triamine referred to abovecan be made by weighing into a 5000 ml. 4-neck flask 1,000 grams ofbenzene, 600 grams of methyl ethyl ketone, 412.68 grams of diethylenetriamine, and 20.0 grams of Dowex 50W-X12 ion exchange resin. The flaskis fitted with a mechanical stirrer, thermometer, Dean-Stark trap, andreflux condenser. The solution is then stirred and heated to reflux.Water is continuously collected and separated in the trap until it canno longer be collected. About 111 grams of water is collected, and thesolution is then filtered and the solvent removed by flash evaporationusing a rotary evaporator under reduced pressure. The remaining liquidis slightly yellow in color with an amine equivalent weight of 79.7(compared to the theoretical value of 82).

EXAMPLE 2

An acrylic copolymer is provided by copolymerizing a mixture of 400grams of n-butyl acrylate, 200 grams of 2-ethylhexyl acrylate, 50 gramsof acrylic acid, 150 grams of methyl methacrylate and 400 grams of theurethane monomer solution prepared in Example 1 in the presence of 40grams of t-butyl peroxy pivalate (75% in mineral spirits) [available asLupersol 11 from Pennwalt Corporation] and 67 grams of isopropanol over3 hours at 80° C. The copolymer was formed in solution at 70% solidscontent in a solvent medium mostly constituted by isopropanol.

EXAMPLE 3

A cationic aqueous disperion of the product of Example 2 is obtained byadding 0.51 gram of 88% formic acid to 100 grams of the product ofExample 2. Low shear agitation is applied to achieve complete mixing ofthe components. Then 110 grams of deionized water are slowly added underhigh shear agitation to obtain a stable white colloidal dispersion at33% nonvolatile solids content.

EXAMPLE 4

The dispersion of Example 3 is modified by the addition of 25% by weightof total resin solids of hexamethoxy methyl melamine. With thisaddition, the dispersion is useful as an aqueous thermosetting coating.It can also be diluted to 10% solids content with additional deionizedwater to provide an aqueous electrocoating bath which electrodepositsupon the cathode of a unidirectional electrical system to provide acoating which resists water washing and which can be baked to cure thesame.

EXAMPLE 5

An anionic aqueous disperion of the product of Example 2 is obtained byadding 4.33 grams of dimethyl ethanol amine to 100 grams of the productof Example 2. Low shear agitation is applied to achieve complete mixingof the components. Then 180 grams of deionized water are added slowlyunder high shear agitation to obtain a stable white colloidal dispersionat 33% nonvolatile solids content.

This dispersion is modified by the addition of 25% by weight of totalresin solids of hexamethoxy methyl melamine. With this addition, thedispersion is useful as an aqueous thermosetting coating. It can also bediluted to 10% solids content with additional deionized water to providean aqueous electrocoating bath which electrodeposits upon the anode of aunidirectional electrical system to provide a coating which resistswater washing and which can be baked to cure the same.

EXAMPLE 6

Another monoethylenic monomer in accordance with this invention wasprepared as follows.

A 1000 ml. 4-neck flask was equipped with thermometer, mechanicalstirrer, reflux condenser, nitrogen inlet, and pressure-equalizeddropping funnel. Into the flask was weighed 111.14 grams of isophoronediisocyanate and 200.0 grams of methyl ethyl ketone. The solution wasstirred and heated to 30° C. under an atmosphere of dry nitrogen.

To this solution was added 122.1 grams of the methyl ethyl ketoneblocked ketimine of diethylene triamine. This ketimine was addeddropwise over 30 minutes and a slight exotherm was observed, so coolingwas used to keep the temperature below 40° C. After addition of theketimine, the funnel was rinsed with 10 grams of additional methyl ethylketone and the mixture was stirred at 40° C. for 30 minutes.

The solution was then warmed to 50° C. and 0.1 gram of dibutyltindilaurate and 0.1 gram of hydroquinone methyl ether were added. This wasfollowed by the addition of 58.05 grams of 2-hydroxyethyl acrylatedropwise over 30 minutes at 50° C. After addition was complete, themixture was diluted with 28.3 grams of methyl ethyl ketone and thetemperature was raised to 70° C. The mixture was stirred at 70° C. untilthere was no NCO absorption in the infrared spectrum, which took about2.5 hours.

The product of this example can be used in the same way to form acopolymer as in Example 2 and then to provide dispersions andelectrocoat baths as in Examples 3, 4 and 5. Corresponding results areobtained.

EXAMPLE 7

Another monoethylenic monomer in accordance with this invention wasprepared as follows.

A 1000 ml. 4-neck flask equipped as in Example 6 was employed. Into theflask was weighed 201.27 grams of alpha,alpha-dimethyl-meta-isopropenylbenzyl isocyanate (meta-TMI monomersupplied by American Cyanamid) and 100.0 grams of methyl ethyl ketone.The solution was stirred and heated to 30° C. under an atmosphere of drynitrogen. To the solution was then added 0.1 gram of dibutyltindilaurate and 0.1 gram of hydroquinone methyl ether.

After soIution was complete, the mixture was treated with 244.11 gramsof the methyl ethyl ketone blocked ketimine of diethylene triamine. Thisketimine was added dropwise over 30 minutes and a slight exotherm wasobserved, so cooling was used to keep the temperature below 40° C. Afteraddition of the ketimine, the funnel was rinsed with 11.31 grams ofadditional methyl ethyl ketone and the mixture was stirred at 35° C. for45 minutes at which point no NCO absorption was detectable in theinfrared spectrum.

The product of this example can be used in the same way to form acopolymer as in Example 2 and then to provide dispersions andelectrocoat baths as in Examples 3, 4 and 5. Corresponding results areobtained.

What is claimed is:
 1. A copolymer of monoethylenically unsaturatedmonomers comprising from 3% to 35% copolymerized monomer which is amonoethylenically unsaturated polymerizable monomer carrying a pluralityof ketimine-blocked primary amine groups.
 2. A copolymer ofmonoethylenically unsaturated monomers as recited in claim 1 in whichthe monoethylenic unsaturation of said monomer carrying a plurality ofketimine-blocked primary amine groups is provided by the acrylate ormethacrylate group.
 3. A copolymer of monoethylenically unsaturatedmonomers as recited in claim 1 in which said ketimine-blocked primaryamine groups are provided by diketimine-blocked diethylene triamine. 4.A copolymer of monoethylenically unsaturated monomers as recited inclaim 1 in which said ketimine-blocked primary amine groups are providedby diketimine-blocked dialkylene triamine in which the alkylene groupscontain from 2-4 carbon atoms, and said monomer carrying a plurality ofketimine-blocked primary amine groups contains acrylate unsaturation. 5.A copolymer of monoethylenically unsaturated monomers as recited inclaim 1 in which said monomer carrying a plurality of ketimine-blockedprimary amine groups is a urethane.
 6. A copolymer of monethylenicallyunsaturated monomers comprising from 3% to 35% of copolymerized monomerwhich is a monoethylenically unsaturated polymerizable monomer carryingblocked primary amine groups and having the formula: ##STR2## in which:R₁ is a divalent organic aliphatic or aromatic molecule connecting thetwo isocyanate groups the residues of which are shown;R₂ is C₂ -C₄alkylene; R₃ is a monoethylenically unsaturated carboxylic acid formingan ester with R₂ ; R₄ is C₂ -C₄ alkylene; and Z is the residue of analiphatic ketone forming a ketimine with the nitrogen atom.
 7. Acopolymer of monoethylenically unsaturated monomers as recited in claim6 in which R₂ is ethylene.
 8. A copolymer of monoethylenicallyunsaturated monomers as recited in claim 6 in which R₄ is ethylene.
 9. Acopolymer of monoethylenically unsaturated monomers as recited in claim6 in which R₃ is acrylic acid or methacrylic acid.
 10. A copolymer ofmonoethylenically unsaturated monomers as recited in claim 8 in which R₃is acrylic acid or methacrylic acid.
 11. A copolymer ofmonoethylenically unsaturated monomers comprising from 3% to 35% ofcopolymerized monomer as recited in claim 6 in which R₂ is ethylene, R₄is ethylene, and R₃ is acrylic acid or methacrylic acid.
 12. A copolymeras recited in claim 6 comprising from 5% to 20% of copolymerized saidmonomer carrying blocked primary amine groups.
 13. A copolymer asrecited in claim 12 comprising acrylate-functional monomer.
 14. Acopolymer as recited in claim 1 made by solution copolymerization andcomprising acrylate-functional monomer.
 15. A copolymer as recited inclaim 14 in which said copolymerization is carried out in water miscibleorganic solvent.
 16. A copolymer as recited in claim 15 dispersed inwater with the aid of a solubilizing acid.
 17. An aqueous coatingcomposition comprising the copolymer dispersion of claim 16 including acuring agent for said polymer.
 18. A copolymer as recited in claim 15comprising copolymerized monoethylenically unsaturated carboxylic aciddispersed in water with the aid of a volatile amine.
 19. Anelectrocoating bath comprising the dispersion of claim 16 having a resinsolids content in the range of from 3% to 20%.
 20. An aqueous coatingcomposition comprising the copolymer dispersion of claim 19 including acuring agent for said polymer.
 21. An aqueous coating compositioncomprising the copolymer dispersion of claim 20 in which said curingagent for said polymer includes blocked isocyanate groups.
 22. Anelectrocoating bath comprising the dispersion of claim 20 having a resinsolids content in the range of from 3% to 20%.